Localization devices have been developed to assist surgeons in performing surgical procedures, e.g., anterior cruciate ligament (ACL) repair procedures. When utilized in an ACL procedure, markers are attached to bones that are observable by a stereoscopic camera system connected to a data processing system that records the positions of the markers in space to establish a coordinate reference system relative to each bone. Additional markers are used to palpate (touch) specific landmarks on the bones in order to ascertain the position of the landmarks in the coordinate reference systems of the bones. A monitor is used to display a representation of the bones that is based on the coordinate reference system and the landmarks for use in guiding a surgeon during the procedure. A description of one particular localization device is described in U.S. Pat. No. 6,385,475 to Cinquin et al., incorporated fully herein by reference.
In one step of the ACL procedure, after a tibial tunnel for receiving one end of a replacement ACL is drilled, the localization device calculates a reference location on a surface of a femur to drill a hole, i.e., a femoral tunnel, in which the other end of the ACL will be attached. Particularly, the femoral tunnel should be placed in a position that will result in the best isometricity for the repaired ACL (i.e., the smallest distance variation between the repaired ACL insertion points in the tibia and femur over the entire range of extension and flexion of the knee joint). A reference location based solely on best isometricity may not be the optimum location for the femoral tunnel. Other criteria must be considered in determining the optimum location of the femoral tunnel. Other points on the femur in the vicinity of the point of greatest isometricity may provide adequate isometricity. Accordingly, a surgeon typically selects an optimum location for the femoral tunnel in the vicinity of the reference location that provides the best compromise between all criteria.
Presently, the surgeon selects the optimum location for the femoral tunnel with the assistance of the localization device. The surgeon positions the tip of a pointer in the general vicinity of the reference location based on instructions from the localization device and his/her knowledge of the procedure. The pointer has a marker that can be tracked by the localization device. The localization device is programmed with data indicating the orientation and position of the pointer tip relative to the marker. By observing the marker, the localization device can determine the position of the pointer tip relative to the surface of the femur.
The localization device displays on a monitor a magnified visual representation of a portion of the surface of the femur including an indicator representing the position of the pointer tip on the surface of the femur. In addition, the localization device displays the isometricity for the position on the femur corresponding to the pointer tip along with information related to other well known criteria for determining the optimum location for the femoral tunnel. Initially, using the visual representation and the displayed isometricity as a guide, the surgeon moves the pointer tip over the surface of the femur to physically locate an area with good isometricity, which will be located in an area surrounding the reference location of greatest isometricity. The surgeon then moves the pointer tip in the general vicinity of the reference location, e.g., within 10 mm, while observing isometricity and other criteria information feedback from the localization device. Finally, the surgeon selects the optimum location for the femoral tunnel based on the observed feedback.
To provide the necessary degree of precision to locate the area in the near vicinity of the reference location and observe points in the general vicinity of the reference location, the magnified visual representation area displayed by the localization device represents an area surrounding the tip of the pointer that is approximately a centimeter in diameter. The actual surface of the bone is relatively large in comparison to the display area and it is difficult to determine the direction the pointer needs to move to reach the reference location, requiring trial and error on the part of the surgeon. Thus, it is cumbersome and time consuming for the surgeon to locate the reference location using the magnified display area.
Accordingly, there is a need for display methods and apparatus to assist in locating reference locations. The present invention fulfills this need among others.